The present invention relates to blends of (a) rubber-modified vinyl chloride resins (PVC), prepared by polymerizing vinyl chloride in the presence of 2 to 20 percent of rubber; (b) copolymers or terpolymers of a vinyl aromatic monomer, such as styrene or p-methylstyrene, an unsaturated dicarboxylic acid anhydride such as maleic anhydride, and an optional third monomer such as methyl methacrylate or acrylonitrile; and (c) optionally 0 to 15 percent of an ungrafted rubber such as a block copolymer of 1,3-butadiene and styrene; and/or 0 to 35 percent of a graft copolymer of rubber, styrene, and methyl methacrylate or acrylonitrile.
Vinyl chloride resins have good molding characteristics, especially when plasticized, and have good physical properties. However, they have a relatively low softening temperature, particularly when they contain a low molecular weight plasticizer, so that they do not have good dimensional stability at temperatures above about 60.degree. C. (or lower) to about 75.degree. C. In the past, various copolymers or terpolymers with higher softening temperatures than a vinyl chloride resin have been blended into the vinyl chloride resin in order to provide good dimensional stability at a higher temperature. The blending of copolymers or terpolymers containing a vinyl aromatic monomer and maleic anhydride, with optionally a third monomer, in order to modify the properties of a vinyl chloride resin or an acrylonitrile, butadiene, styrene polymer has heretofore been described in various patents.
U.S. Pat. No. 3,642,949 describes blends of copolymers of styrene and maleic anhydride (S/MA) with ABS graft copolymer (rubber-modified copolymer of styrene and 5 to 40 percent of acrylonitrile, prepared by polymerizing the monomers in the presence of rubber) in order to increase the softening temperature of the latter. The S/MA copolymers contained 5 to 35 percent of maleic anhydride, preferably 18 to 25 percent, and were not rubber-modified.
U.S. Pat. No. 3,626,033 describes the preparation of blends of a S/MA copolymer, a vinyl chloride resin, and a high-rubber ABS graft copolymer containing at least 50 percent of rubber. The styrene-acrylonitrile (S/AN) copolymer preferably contained 24 to 48 percent of acrylonitrile, while the S/MA copolymer contained 15 to 30 percent, and preferably about 19 percent, of maleic anhydride. This patent also decribes the preparation of blends of vinyl chloride resin, a S/MA copolymer containing 18 percent of maleic anhydride, and a graft copolymer reported to be a copolymer of methyl methacrylate and acrylonitrile. S/MA copolymers were effective in increasing the softening temperature of the blends. For example, a blend of a vinyl chloride resin and an ABS resin in a 75:25 ratio exhibited a heat distortion temperature of 77.5.degree. C., compared with a 71.5.degree. C. vinyl chloride resin alone. A three-component blend containing 20 percent of an unmodified S/MA copolymer (containing 18 percent of maleic anhydride), together with a vinyl chloride resin and an ABS resin in the same ratio as in the two-component blend, exhibited a heat distortion temperature of 91.degree. C. However, notched impact strength was reduced.
U.S. Pat. No. 4,197,376 describes the preparation of blends of ABS graft copolymers with (a) rubber-modified copolymers of 85 to 65 percent of styrene and 15 to 35 percent (preferably 20 to 30 percent) of maleic anhydride and 2 to 30 percent of rubber (based on total weight of the composition), and (b) rubber-modified terpolymers of styrene, maleic anhydride, and up to 30 percent of a copolymerizable monomer such as methyl methacrylate (S/MA/MM) or acrylonitrile (S/MA/AN). The blends contained 5 to 40 percent of rubber (based on the total weight of the composition). Such blends exhibited better impact strength than blends of unmodified S/MA copolymer and ABS, or of rubber-modified S/MA copolymer with unmodified S/AN copolymer, even when the blends were compounded to the same total rubber level.
U.S. Pat. No. 4,311,806 describes the preparation of blends of a vinyl chloride resin with rubber-modified S/MA copolymers in which the relative weight proportions were 50 to 85 percent of a vinyl aromatic monomer, 15 to 30 percent of maleic anhydride, and 0 to 20 percent of a third monomer such a methyl methacrylate or acrylonitrile. The monomers were polymerized in the presence of 5 to 25 percent by weight of rubber (based on total weight). The blends could optionally contain 0 to 40 percent of ABS graft copolymers or MBS graft copolymers (rubber-modified copolymers of styrene and methyl methacrylate). Again, the copolymers containing maleic anhydride were effective in increasing the heat softening temperatures. The addition of the vinyl chloride resin to the rubber-modified terpolymer caused a large reduction in impact strength. The reduction was less when about 20 percent of ABS resin or MBS resin was added to the blend.
U.S. Pat. No. 4,339,554 describes the preparation of blends of a vinyl chloride resin with 20 to 40 percent of S/MA copolymers containing preferably 18 to 25 percent of maleic anhydride. Blends were also described which contained the corresponding rubber-modified copolymers, which had been prepared by polymerizing the monomers in the presence of 5 to 30 percent of one or more rubbers, based on total weight of the rubber-modified copolymer.
Hall, Kruse, Mendelson, and Trementozzi (Preprint for Organic Coatings and Plastics Chemistry Division, Volume 47, page 298; Meeting of Am. Chem. Soc., Sept. 12-17, 1982) described the formation of blends of various random S/MA/X terpolymers (both rubber-modified and unmodified versions) with random styrene-acrylonitrile (S/AN) copolymers or ABS graft copolymers. The termonomers were acrylonitrile, methyl methacrylate, isobutylene, methyl acrylate, and ethyl acrylate. They defined composition ranges for S/AN copolymers, S/MA copolymers or S/MA/X terpolymers within which blends exhibited compatibility. Compatible pairs exhibited softening temperature (glass transition temperatures) intermediate between those of the two components. Data for blends of ABS and S/MA/X terpolymers were summarized from U.S. Pat. Nos. 4,197,376 and 4,305,869.
British Pat. No. 2,015,007, which is incorporated into this disclosure by reference, discloses blends of vinyl chloride resins with block copolymer rubbers of a diene and a vinyl aromatic monomer, together with up to 20 percent of an impact modifier: (a) MBS, a graft copolymer of methyl methacrylate, a butadiene-based rubber, and styrene; or (b) ABS, a graft copolymer of acrylonitrile, a butadiene-based rubber, and styrene. Blends of rubber-modified vinyl chloride resins with block copolymer rubbers were also disclosed. In both types of blends, the block copolymer rubbers increased impact strength, particularly at low temperatures after aging.